Field of the Invention
The present invention relates to audio processing techniques in devices having drive mechanisms.
Description of the Related Art
Image capturing apparatuses such as digital cameras and digital video cameras record moving image data that is shot, along with audio data from the surroundings of a subject. Sound from the surroundings of a subject to be recorded will be called “surrounding environment sound” hereinafter.
An image capturing apparatus can also focus and zoom in on a moving subject while shooting by moving an optical lens. Optical lenses are moved mechanically, and moving the lens produces driving noise. If this driving noise overlaps with the surrounding environment sound, the quality of the audio in the moving image will be poor.
Japanese Patent Laid-Open No. 2006-279185 and Japanese Patent Laid-Open No. 2011-114465 are known documents disclosing techniques for reducing such noise.
Japanese Patent Laid-Open No. 2006-279185 discloses a spectral subtraction method. Put simply, the spectral subtraction method works as follows.
First, frequency spectrum data is generated by applying a Fast Fourier Transform to time-series audio data obtained from a microphone. Frequency spectrum data expressing driving unit noise, which is prepared in advance as a noise profile, is then subtracted from the original frequency spectrum data. The result of this subtraction is then subjected to an inverse Fast Fourier Transform (iFFT) to generate time-series audio data with the noise removed.
However, the driving signals output from driving units differ to varying degrees from product to product. Thus the noise defined by a single noise profile may not perfectly match the noise produced by the driving unit of an actual product, which means that sound aside from the noise may be removed from the surrounding environment sound.
In Japanese Patent Laid-Open No. 2011-114465, the image capturing apparatus is provided with not only a microphone for the normal surrounding environment sound, but also a microphone for noise detection. Thus according to Japanese Patent Laid-Open No. 2011-114465, the image capturing apparatus includes a first microphone for obtaining sound from outside the apparatus and a second microphone for obtaining noise produced inside the apparatus. The first microphone outputs an audio signal of the audio outside the apparatus, and the second microphone outputs a noise signal expressing driving noise produced within the apparatus. The image capturing apparatus reduces noise in the audio signal by a process for subtracting the noise signal from the audio signal.
However, with the method disclosed in Japanese Patent Laid-Open No. 2011-114465, a microphone for obtaining noise must be provided in addition to the microphone for obtaining the surrounding environment sound, which is problematic due to increased costs, required surface area, and so on. Although Japanese Patent Laid-Open No. 2011-114465 describes a configuration in which monaural audio is obtained, an apparatus that obtains stereo audio, for example, will require a total of three microphones, i.e., two for recording audio in stereo and one for noise.